The Difference Between Camshafts and Crankshafts

Where to Find the Camshaft

The camshaft is located either at the top of the engine—known as an overhead cam—or within the engine block. It opens and closes the valves that let air and fuel into the combustion chamber while permitting exhaust gasses to leave.

An inline-six cylinder engine with the valve cover off, exposing the camshaft.

Today’s internal combustion engines have up to four camshafts, depending on the design and number of cylinder heads. The number of valves per cylinder varies, depending on the vehicle. However, all cylinders contain a mixture of intake and exhaust valves that are operated by the camshaft.

How a Camshaft Works

The crankshaft drives the camshaft, and the camshaft transfers motion from the crankshaft to the valvetrain to open and close the valves. A camshaft has a number of egg-shaped cam lobes that, as they turn with the camshaft, act upon the valvetrain. Cam lobes vary in size and shape to allow complete control over when and how long the valve remains open.

A four-cylinder double overhead cam (DOHC) Honda cylinder head

The camshaft and crankshaft gears are connected by a timing chain or belt, or sometimes via a meshed gear set at the motor’s front end. Through the four-stroke combustion cycle (intake, compression, combustion, and exhaust), the crankshaft turns two times—every piston goes up and down twice.

However, the camshaft turns only once during each combustion cycle, and each valve opens once. This ensures that the intake valve is open on the intake stroke and the exhaust valve is open on the exhaust stroke. The valves stay closed during the compression and combustion strokes.

How a Camshaft Is Different From a Crankshaft

Here are the main differences between the two components:

• Material – The crankshaft is usually made from forged alloy steel, while the camshaft is usually cast steel or iron.
• Purpose – The crankshaft converts up-and-down piston motion into rotary motion while the camshaft opens and closes the intake and exhaust valves at the appropriate times.
• Location – The crankshaft is below the cylinder, while overhead cams are above the cylinder. Cam-in-block camshafts for pushrod engines are typically mounted above the crankshaft.
• Power source – The crankshaft rotates due to the downward movement of the pistons during the combustion process, while the camshaft rotates due to the timing belt or chain attached to the crankshaft.

Symptoms of a Bad Camshaft

A bad camshaft can extensively damage the engine, cylinder head, and crankshaft. That’s why watching for early signs of failure like these is essential:

• Check engine light – Check the code in the onboard computer to determine if it’s a problem with the camshaft.
• Power loss – If the valves aren’t opening and closing at the correct times, you may notice a drop in power, especially during acceleration.
• Backfiring – If the timing is off, you could get backfiring or misfiring.
• Ticking or tapping noises – These sounds come from excessive movement due to a problem with the camshaft.
• Metal debris in the engine oil – If something has broken loose.

Some of these symptoms can also indicate a bad camshaft position sensor, which is much easier and cheaper to replace.

If a camshaft breaks, it can further damage the engine, valvetrain parts, cylinder head, block, crankshaft, connecting rods, and pistons. Aside from the damage, the vehicle won’t start or run when it breaks.

How to Replace the Camshaft

Replacing a camshaft isn’t a job for a novice. We recommend reading your factory service manual for the proper procedures related to your vehicle.

An engine block on the workbench, with the crankshaft exposed.

If you have the time and tools to tackle the job, here is the basic process.

First, you want to gather all of your supplies:

• New camshaft
• Floor jack and jack stands
• Wheel chocks
• Ratchet with extensions and sockets
• Pry bar
• Torque wrench
• Valve cover gasket

With your equipment nearby, continue onto these steps.

1. Jack up the vehicle and secure it on jack stands.
2. Remove the parts necessary to reach the camshaft. These steps are outlined in your service manual.
3. Rotate the engine with the crankshaft pulley bolt until the camshaft timing marks line up.
4. Take off the timing belt or chain.
5. Remove the camshaft(s) and install replacement to manufacturer specifications.
6. Align the timing marks and reinstall belt or chain.
7. Rotate the engine to check the timing alignment.
8. Reinstall any parts that were removed in reverse order.

Start the engine and make sure everything sounds as it should. Watch for any leaks before heading out on the road.

Camshaft Replacement Cost

On average, you may spend $350 to $800 for a new camshaft. You’ll dodge a hefty repair bill if you can replace it yourself. Otherwise, expect to pay about $1,250 to $2,000 on labor charges. These estimates depend heavily on your vehicle type and where you live.

If the failure causes other damage, those repair costs will be added to the price. For example, if you need to replace the cylinder head, you have another substantial bill to consider. At worst, you may need to rebuild or replace the entire engine.